I'd make sure my team mates distract him first. BTW, is it for the single player campaign, or multiplayer? We have tags for both, single-player and multiplayer respectively.
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Martin SojkaNov 10 '11 at 11:59

To add to this: If you're close enough to the chopper, then you can fire your stinger before they use their flares and they either won't have enough time to deploy flares, or even if they do, the stinger is too close to miss them.
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Mr SmoothNov 10 '11 at 13:34

I just had the most annoying chopper pilot. 1500 tickets map, didn't die once. Just flew low to avoid tracking and lock-on, if it worked, took forever because of his chopper upgrades (at least it felt like it) - though I was probably the only one shooting at him
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Christian StrangNov 10 '11 at 13:55

This is by far the easiest approach to taking down air vehicles, as soon as the pilots hear the lock on tone they pop flares.
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Jamie KeelingNov 10 '11 at 23:50

Do you fire it immediately after he fired the IR-flares (because that causes the missile to still follow the flares, at least sometimes) or do you wait a few seconds?
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Christian StrangNov 11 '11 at 0:28

1

good catch! I wait for the flares dissipate a bit, then fire.
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DrFishNov 11 '11 at 7:44

My answer would be to either fire only when they are too close for countermeasures to be effective or use a non targeting anti-armour solution (RPG, SMAW) while this may not be easier they cannot be redirected by countermeasures. I like Bora's idea however it is very inconsistent and I wouldn't rely on it.